Similarities and differences in cerebellar grey matter volume and disrupted functional connectivity in idiopathic Parkinson's disease and multiple system atrophy.

•Similar alterations of cerebellar GMV and DN FC were observed in the IPD and MSA groups.•More widespread impairment of cerebellar GMV and DN-DMN FC were found in MSA compared with IPD.•Decreased intracerebellar FC was associated with GMV loss in MSA but not in the IPD group.•A composite connectivity/atrophy score was related to motor and cognitive symptoms in MSA group.